Enhancing soil redox dynamics: Comparative effects of Fe-modified biochar (N-Fe and S-Fe) on Fe oxide transformation and Cd immobilization

Tianren Si; Rui Yuan; Yanjie Qi; Yuhao Zhang; Yan Wang; Rongjun Bian; Xiaoyu Liu; Xuhui Zhang; Stephen Joseph; Lianqing Li; Genxing Pan

doi:10.1016/j.envpol.2024.123636

Enhancing soil redox dynamics: Comparative effects of Fe-modified biochar (N-Fe and S-Fe) on Fe oxide transformation and Cd immobilization

Environ Pollut. 2024 Apr 15:347:123636. doi: 10.1016/j.envpol.2024.123636. Epub 2024 Feb 22.

Authors

Affiliations

¹ Institute of Resources, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, 1 Weigang, Nanjing 210095, China; Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, China.
² Institute of Resources, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, 1 Weigang, Nanjing 210095, China; Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, China; School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia.
³ Institute of Resources, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, 1 Weigang, Nanjing 210095, China; Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, China. Electronic address: lqli@njau.edu.cn.

PMID: 38401634
DOI: 10.1016/j.envpol.2024.123636

Abstract

Biochar and modified biochar have gained wide attention for Cd-contaminated soil remediation. This study investigates the effects of rape straw biochar (RSB), sulfur-iron modified biochar (S-FeBC), and nitrogen-iron modified biochar (N-FeBC) on soil Fe oxide transformation and Cd immobilization. The mediated electrochemical analysis results showed that Fe modification effectively enhanced the electron exchange capacity (EEC) of biochar. After 40 days of anaerobic incubation, compared to the treatment without biochar (CK), the concentrations of CaCl₂-extractable Cd in N-FeBC, S-FeBC, and RSB treatments decreased by 79%, 53%, and 23%, respectively. Compared with S-FeBC, N-FeBC significantly decreased the soil Eh and increased soil pH within the first 15 days, which could be attributed to its higher EEC and alkalinity. There is a negative correlation between the concentration of CaCl₂-extractable Cd and soil pH (p < 0.01). The sequential extraction results showed that both N-FeBC and S-FeBC promoted Cd transfer from acid-soluble to Fe/Mn oxides bound fraction (Fe/Mn-Cd). N-FeBC significantly increased the concentration of amorphous Fe oxides (amFeox) from 4.0 g kg^-1 in day 1 to 4.6 g kg^-1 in day 15 by promoting the NO₃^--reducing Fe(II) oxidation process, while S-FeBC significantly increased amFeox from 4.0 g kg^-1 in day 15 to 4.8 g kg^-1 in day 40 by promoting the Fe(II) recrystallization. There is a positive correlation between the concentration of amFeox and Fe/Mn-Cd (p < 0.01). The scanning electron microscopy analysis showed that Cd was bound to the amFeox coating on the surface of Fe-modified biochar. By acting as an electron shuttle, the active surface of Fe-modified biochar may serve as a hotspot for Fe transformation, which promotes amFeox formation and Cd immobilization. This study highlights the potential of Fe-modified biochar for the remediation of Cd-contaminated soils and provides valuable insights into the development of effective remediation approaches for Cd-contaminated soils.

Keywords: Cd; Fe oxide; N–Fe modified biochar; Redox process; S–Fe modified biochar.

MeSH terms

Cadmium / analysis
Calcium Chloride
Charcoal / chemistry
Ferrous Compounds
Iron / chemistry
Oxidation-Reduction
Oxides / chemistry
Soil Pollutants* / analysis
Soil* / chemistry

Substances

biochar
Soil
Cadmium
Oxides
Calcium Chloride
Soil Pollutants
Charcoal
Iron
Ferrous Compounds